Many semiconductor heating processes require a wafer to be heated to high temperatures so that various chemical and physical transformations can take place as the wafer is fabricated into a device. During rapid thermal processing, for example, semiconductor wafers are typically heated in a thermal processing chamber by an array of energy sources to high temperatures, such as from about 100xc2x0 C. to about 1,200xc2x0 C., for a time that is typically less than a few minutes.
Besides heating semiconductor wafers, thermal processing chambers are also used to chemically react wafers with other components, such as gases. For instance, various gases can be circulated through the thermal processing chamber to react with the surface of the semiconductor wafer during heating to form a desired film or coating on the wafer. For example, steam can be present within the chamber to form oxidation coatings on the wafer. Reactions of this type may be carried out under pressure or under vacuum conditions. Thus, it is often necessary to isolate the thermal processing chamber from the energy source by a window. This window is typically formed of a material that allows for effective transmission of heat energy and that withstands processing pressures.
In the past, these windows were conventionally formed from thin, solid quartz plates. However, one problem with such thin quartz plates is that they possessed an inherently poor mechanical strength to withstand the bending stresses that result from vacuum or fluid pressures generated inside the thermal processing chamber during the heat treatment of a wafer.
Consequently, solid quartz plates having a relatively large thickness have also been utilized. However, one problem with such thick, solid quartz plates is that the plates are difficult to cool after heat treatment is terminated. In particular, after a wafer is heated for a desired time, the light source is immediately shut down so that the wafer can cool very quickly. Unfortunately, due to the relatively low heat conduction coefficient of these thick quartz plates, the window fails to cool down as fast as the wafer and thus, continues to irradiate heat energy back to the wafer. Moreover, as the wafer heats up, it also irradiates energy back to the quartz window. This heating of the wafer and quartz plate continues until a stable temperature is reached. The phenomenon described above, which is often called the xe2x80x9cfirst wafer effectxe2x80x9d, can substantially decrease the efficiency and throughput of the system, adversely affect the achievement of repeatable uniformity of the wafer temperature, and place a burden on the temperature control system.
As such, a need currently exists for a window that has the strength to withstand processing requirements without substantially effecting the efficiency of the system.
In accordance with one embodiment of the present invention, an apparatus for heat treating a substrate, such as semiconductor wafer is provided. The apparatus includes a thermal processing chamber and a energy source in communication with the chamber. Further, the apparatus also contains a window that contains a member having a first side facing the substrate and a second side facing the energy source. In some embodiments, the window has a thickness greater than about 1 inch so that it can withstand certain pressures applied during processing. Moreover, the window can also contain a material, such as quartz or sapphire, that is capable of allowing thermal radiation at a preselected wavelength to pass therethrough. Moreover, the first member defines at least one passage that is capable of being placed into communication with at least one coolant, such as air, water, an emulsion, etc. The coolant can, in some embodiments, cool the window at a faster rate and thereby inhibit the onset of the xe2x80x9cfirst wafer effectxe2x80x9d.
In accordance with another embodiment of the present invention, a method for heat treating a semiconductor wafer is provided. The method includes providing a heat treating apparatus that contains a thermal processing chamber, an energy source, and a window. The method also includes heating the semiconductor wafer to a certain temperature and, after the temperature is reached, terminating the heating of the wafer. Moreover, the method also includes supplying at least one coolant to at least one passage defined by a first member of the window.
Other features and aspects of the present invention are discussed in greater detail below.